The capability used for managing tags should be separate from that for categories

Description

The capability used for managing categories is manage_categories. Guess what it is for managing tags? It's not manage_tags, nor manage_post_tags. It's manage_categories too.

This causes a problem when you're trying to control capabilities for tags and categories separately.

The patch to change the capability for tags to manage_post_tags is a simple one, but it could potentially introduce an issue where people who have the manage_categories capability would no longer be able to manage tags.